What is the tonic in a musical scale?

The tonic in a musical scale is indeed the key note of the scale. It serves as the foundation upon which the rest of the scale is built and is often referred to as the 'home' note. The tonic defines the key of the piece, meaning that other notes in the scale relate to it in terms of harmony and melody. When musicians create music, they often resolve melodies or chords back to the tonic, creating a sense of completeness and stability.

In contrast, the second note of the scale, the fifth, and the last note do not fulfill the same foundational role that the tonic does. The second note can often serve as a step or passing tone, the fifth note is important for creating the dominant function, and the last note in the scale does not designate a specific tonal center or key identity. Thus, the tonic's position as the key note is what establishes it as the heart of the scale.